Hollow-core panel



Aug- 23, 19.49- w. H. RUNDQUlsT I 2,479,870

HOLLOW-CORE PANEL Filed NOV. 2, 1945 2 Sheets-Sheet 1 amati 'vw,

y far/eey Aug. 23, 1949. w. H. RUNDQUIST HOLLOW-CORE PANEL 2 Sheets-Sheet 2 Filed Nov. 2, 1945 Patented Ang. 23, 1949 U'EED STATES PTENT FFICE mit??? noLLovV-CORE PANEL Winans n. Rnn'aqnisnneek Island, ing,fnjs's'igne to Rock Island Millwork Company, a corporation of Illinois Anniieetien November 2, 1945, serial ne. szaeid. Claims. (o1. y'2t-91) This invention relates vgenerally to improvements in panels, and in particular to hollowcore door constructions.

Flush solid-core doors as generally made heretofore are relatively heavy, as compared with paneled doors or the like of equalsize, due to the greater quantity of material employed in their manufacture. In addition, solid-core flush doors as heretofore made have rendered them subject to Warpage under varying climatic and atmospheric conditions.

It is an object of the present invention to provide a flush hollow-core door or like structure so constructed that it not only is lighter in Weight, as compared with a solid structure, such as a ilush solid-core door of conventional construction, but one that is stabilized to a substantial degree against distortion resulting from varying conditions of humidity.

In all or most Wood Working mills, such as sash and door plants, there are left-over pieces yof wood that are classed as core blocks. The core blocks from certain operations may be madeup of pieces more or less uniform as to Width and thickness, but varying in length. It is another object of the present invention to provide an improved iush door or other panel-like strucf ture having a core that may be made up of such heretofore short and narrow pieces of lumber, and which door, While of sturdy construction, also is substantially less in Weight than conventional solid flush doors of like dimensions. Reduction in weight of such doors is important, not only from the standpoint of the reduction .of stresses on hinges and frames and of thereduction of eort required in swinging them in use, but also from the standpoint of thereduce tion in handling and shippingcosts from the point of origin to jobbers and users. a

Another object of the invention is to provide a ush door having a core that provides internal ventilation substantially throughout the Width and length of the door, not only forfacilitating the drying and settingof the glue employed in the manufacture of the door, but for the purpose of subjecting internal surfaces of the door structure to conditions of humidity similar to those that aifect the outer surfaces for thereby neutralizing, in substantial degree, the forces that generally produce distortion of large wood panels.

Other objects of the invention relate to various features of construction and arrangement of parts that Will be apparent from a consideration of the following speication and accompanying drawings, ,v'vherein n .i

Fig. lisa .brokenffront elevation of a panel construction such a lushhollow-core door that ie illustrative, if ,the present invention.

Y Fi'g. 2 isan enlarged sectional View taken on line 2 2 o'f Fig. 1. M Fig. 3 is an enlarged line 3-3 of Fign 1`. i a

4 isa 4broken perspective view `illustrating a core structure in an initial state of manufacture.

Fig. 5 is 'a broken perspective View of a detached eene4 sdnfeture; Fig. 6.isa bijokensideelevation o fa door showing in 'position therein a modied core structurel ,Figl Tis-anenlarged setionalaview taken on line l-.1 of Fig. lG a'nd illustrating the modified core.structur..- ,A ,y F'gn isa broken vertical longitudinal sectional vieu/.of ,a .usli-typebupboard door, taken on a line intermedatehorizontal stiles, and illustrative ofthe prsent invention.4 ,Y

sectional View taken on In tne 1fawing. the deer nnen/n inV Fig. 1, fer

the purpose of illustrating 'the preferredwuse ,of the invention, is provided with a surfacecovered.structurecomprising edge strips, preferably arranged to 'formlafrarfne I0, with or Without joined. corners; including upper and `lower rails `I, st`il's` anda core structure. I3. As shown, the dimensions of the frame correspond to the Widtli and.'lii`gth of. the doonmThe rails and Stiles .may be unitl'edat thecorners of the frame bydowelsfgby .mrti'se' and tenonjoints, or by any etnefsnitabie mens; not shewn. Y

Thecoresl` oture Itisno'f the required lengthand crosswis'dimensions;tojfit within vthe fanfie i0; and ir 4theDelfiv'lilar structure illustrate`d,'the c'reisattaffedto thefrarneby staples i4. Thiit oflth core Withinthe frame need not be' precise ndr. need the staples afford any subs'tantial V,rigidityto' the `structure inasmuch as they arey employediinthe initial assei'nblyl pri- Iarily for' retaining* the `I'Jarts 'together during the subsequent manufacturingstages.,

The core structureI I3'1`nay beima'de, and for thepurpose ofeconornypreferably is made, of available material.thatnightothe'rwise beclassed as scrap. indicated Fig'li'jthe core initially is assembled inslal'i forn'by-gluing together at the edges a number of relatively -shortpiecesnof l't'l'rl'kieir f5V Whilipiefably are' substantially uniform in' vvidthand thickness or which can be inad's by economicalmill operations. Such pieces of lumber indicated in Fig 4, generally are of random or non-uniform length whereby the end joints of the pieces in the assembled slab are staggered. It is not necessary that the blocks in the assembly provide two planar surfaces as blocks of different heights from an assembly table top are permitted. Lengths also may vary. After removal from the glue-up clamps, the composite slab is run through a resaw then run through a moulder which reduces it to a uniform or other condition of desired thickness corresponding to the thickness of the frame I0. At the same operation, one set of longitudinal grooves or channels is formed in each of the opposite faces, preferably all in one direction as illustrated by grooves I6. The slab is then grooved on each face by a new set crossing the first set, as by passing it through a gang'grooving machine which cuts transverse grooves in each face of the slab as shown at I'I in Fig. 5. The two sets of grooves I6 and I1 of each face are preferably uniformly spaced to provide regularly distributed studs or blocks I8 that are integral with a medial web I9, preferably centered between the faces of the cut slab.

In the structure shown in Figs. 1, 2 and 3, sheets are secured to opposite sides of the frame and core structures which impart to the door its flush character. Where a Wood grain at the surface is desired, veneer is suitable and it is preferably cross-banded by an inner ply of wood to provide relatively crossing grains. As illustrated in said figure, there are glued to the respective co-planar end-surfaces of the studs I8 and to the corresponding faces of the frame I0, on each side of the door, a cross-banding wooden sheet 2! that may be a ply of wood veneer approximately l-s" in thickness and having the grain extending crosswise of the frame. Such cross band having the grain extending crosswise of the door, offers substantial resistance to dimensional changes in the door in a transverse direction. To the outer surface of each crossband 2li, in the form of the door shown in Fig. 1, there isglued a finishing or facing sheet of veneer 2l with grain lengthwise of the door. The facing sheets, which may be of a selected wood, such asV hard wood, give the door the desired surface appearance and may be nished as desired. Any wood ply covering may be one or more pieces arranged as desired.

In gluing the crossbands, with or without the outer veneer sheets, to the frame and core as mentioned above, the coplanar surfaces of the studs and the faces of the frame receive the glue. As will be noted, each of the studs I8 at one side of the web I9 is arranged directly opposite a stud on the other side, and hence substantial pressure may be exerted on the assembly by the Dress during the gluing of the crossbands to the frame and core or of the veneer to the already glued-on crossband, Without producing distortion of the web I9 or the sheets carried by its studs I8. The crossbands 28 thus are secured along the margins to the frame I and are attached at numerous intermediate, and preferably regularly disposed, areas or spots to the studs I8.

It will be understood that the core structure I3 of a particular door need not be composed .of a single slab, but may consist of two or more preformed slabs, each preferably extending across the opening of the frame and initially secured to the frame by staples.

Preferably, ventilation passages are provided in the frame I0, which communicate with the core channels I6 and Il on each side of the medially midty affecting opposite sides of the core.

.4 disposed web I9, as shown at 22 in Figs. 1, 2 and 3. The passages 22 may be in the form of transverse grooves formed in the surfaces of the upper and lower frame rails I I. These ventilation passages are visible only at the ends of the door and are not, therefore, objectionable from the standpoint of appearance, but they facilitate the drying or setting of the glue used in attaching the crossband to the core, and thereby shorten the conditioning period that is usually required between completion of the manufacture of the doors and the shipping of the same. Likewise, the passages 22 permit the inner door structures to breathe with temperature changes, and to take on or give up moisture under Varying conditions of humidity that affect the outer surfaces of the door and they thus tend to effect equalization of those forces which produce warpage of wood struct-ures. As many ventilation passages may be provided in the frame rails as desired. In spite of the fact that the structure is one to minimize or prevent warping, the minimizing of warp-inducing forces lessens the stresses imposed within the structure.

The web I9, being relatively thin, exerts but small warpage forces, even should conditions obtain wherein one side of the web contains much more moisture than the other. The studs IB themselves, being of relatively small crossgrain dimensions, expand or contract inappreciably under the influence of humidity changes. Because the core is formed by numerous pieces I5 of wood glued edge-to-edge and has random disposition of annular rings, the tendency of some pieces to warp in one direction is substantially `resisted by the opposite tendencies of other pieces,

Vand hence the core itself is substantially stabilized against distortion, due to differences in the hu- The crosswise forces exerted by the web I9 in tending to expand or contract transversely are of low degree, due to the relative thinness of the web. Such forces are resisted by the crossbands or other surfacing sheets, and hence the improved door not only is relatively light in weight, as ccmpared with a solid type flush door of similar dimension, but it is substantially more stable with respect to dimensional changes when subjected to variations in humidity or climate conditions. In the core, the ends of blocks I5 (Fig. 4) exhibiting ends of grain, are not effectively glueable, and hence, commonly no glue is applied. Thus, there are formed unglued joints in the midweb IS at these locations. Moisture vapor inside the core channels can thus readily penetrate the midweb through these unglued joints, thus further to minimize humidity dierences.

In Fig. 6 a door is illustrated which may be manufactured as above described and comprises a frame 23, a core 24, erossbands 25, and facing sheets 25. The core 24 has studs 27, as shown more clearly in Fig. l, which are not oppositely arranged as in Fig. 1, but are staggered, that is, the studs on the reverse side of the core in Fig. 6 are arranged opposite the areas of intersection of the channels on the obverse side of the core. In this arrangement, it is preferred that the channel spacing be at least equal to or greater than the channel width, so that assembly pressure on a stud is not born by a span of the medial web. The staggered arrangement provides parallel longitudinal channels 28 and transverse circulation channels 29 on each side of the web 33. While this construction does not possess the resistance to compression while in the glue presses that is afforded by the arrangement of Fig. 1, the

staggered relation of th studs impr'ves the insulating value 'of the constructioiito some extent by interrupting dire'rcthef -i'low paths from one face of the dopr to the eter, which are present where the studs are ppositely arranged. Ventilation passages 3l iny vthe framexrails preferably are provided as in the above described structure.

In Fig. 8 a door, `commonly designated a cupboard door, is shown in broken longitudinal section. The core 32 issimilar to the core I3 above described with respect to Fig. 1, but to each face of the core and a flange-forming frame 33 is attached a sheet of pre-formed B-ply-ply'wood 321, in lieu of the two pieces of crossbands and veneer sheets above described. The plywood sheets rigidify the structure and are attached to the core and frame by glue, with suitable compression. The crossband and venee'rrsheetsmay of course be used in making flush cupboard or other doors, or panels, if desired', While pre-formed plywood sheets of suitable wood may be substituted for the useof separatel crossband and veneer sheets, as described for the larger flush doors of Fig. 1.

In utilizing the prsent improvements in small doors, such as cupboard doors, I Vhave found that the web 'of a 3pinch-thick Acore need not be thicker than 1A; inch and if the studs are 3A; inch square and the channels 3A inch wide, with a crossband lg inch thick and facing veneer 1A; inch thick, the structure is suitably rigid. In doors of larger sizes such as room doors, the thickness of the core and other dimensions of the parts are greater. iSoit Wood, as pine for example, is suitable for the core, and waterproof or waterresistant glue preferably is employed in the gluing operations mentioned. However, any glue may be used, and hot pressing of resin glues may be practiced.

The wood ply coverings, or the plywood surface, are examples of a reinforcing sheet material attached to and rigidifying the otherwise flexible core structure. Such a sheet secured to two spaced studs, for example, acts as a rigidifying bridge, and although the sheet-bridge itself may be of flexible material, such as wood veneer, the medial web of the core and the sheet act mutually to resist flexure of each other, and hence to prevent warping. Thus, for a non-warping panel, the core structure and the surfacing sheets are sufficient in the combination described, and the perimetrical frame among other uses, provides finished edge structures where the margins of the covering sheets are secured to the frame.

Although the doors or panels have been illustrated as each of uniform thickness, it is to be understood that there is no essentiality in the two planar sides being parallel.

While I have shown and described door structures which are illustrative of the improvements, the invention may be utilized in other panel structures, and changes in the details shown may be resorted to within the scope and spirit of the invention, as set forth in the appended claims.

I claim:

1. A panel suitable for use as a door comprising in combination a rectangular perimetric frame of wood, a core structure disposed within the frame and tting closely in the frame opening, said core structure having its bounding faces co-extensive with the faces of said frame, said core structure consisting of multitudinous pieces of wood placed together endwise and sidewise and glued into a unitary body, said pieces having their grainsrunring generally in the saine direction and in the plane of the extent of th'e core structure, said pieces being in random arrangement of the annular rings of the individual pieces, 'said structure being provided with series of crossing channels in each face to a limited depth whereby to provide a relatively thin planar midweb in the core structure, and to provide 'on each face a plurality of columnar studs projecting from said midweb to the respective bounding faces of the core structure, and sheet material secured to ea-ch of the faces of the frame and to the correspond'- ing end-faces of the studsl V t l 2. A panel suitable for use as a doorcomprising in combination a rectangular perimetrictframe of wood, a core structure disposed within the frame and 'fitting closely inthe frame opening, said core structure having its bounding faces co- `extensive with the faces of said frame, said core structure consisting of multitudinous pieces of wood placed together endwise and sidewise and glued into a unitary body, said pieces having their grains running generally in the same direction and in the plane of the extent of the core structure, said pieces being in random arrangement of the annular rings of the individual pieces, said structure being provided with longitudinal and transverse channels in each face to a limited depth whereby to provide a relatively thin planar rndweb in the core structure, and to provide on each face a plurality of columnar studs of rectangular cross-section projecting from said midweb to the respective bounding faces of the core structure, and sheet material secured to each of the faces of the frame and to the corresponding end-faces of the studs.

3. A wooden panel suitable for use as a door comprising in combination a rectangular perimetric frame of wood, a core structure disposed within the frame and fitting closely in the frame opening, said core structure having its bounding faces co-extensive with the faces of said frame, said core structure consisting of multitudinous pieces of wood placed together endwise and sidewise and glued into a unitary body, said pieces having their grains running generally in the same direction and in the plane of the extent of the core structure, said pieces being in random arrangement of the annular rings of the individual pieces, said structure being provided with longitudinal and transverse channels in each face to a limited depth whereby to provide a relatively thin planar midweb in the core structure, and to provide on each face a plurality of columnar studs of rectangular cross-section proj ecting from said midweb to the respective bounding faces of the core structure, and at least two layers of cross-banded wood veneer secured to each of the faces of the frame and to the corresponding end-faces of the studs.

4. A panel suitable for use as a door -comprising in combination a, rectangular perimetric frame of wood, a core structure disposed within the frame and fitting closely in the frame opening, said core structure having its bounding faces co-extensive with the faces of said frame, said core structure consisting of multitudinous pieces of wood placed together endwise and sidewise and glued into a unitary body, said pieces having their grains running generally in the same direction and in the plane of the extent of the core structure, said pieces being in random arrangement of the annular rings of the individual pieces, said structure being provided with longitudinal and transverse channels in each face to a limited depth whereby to'provide a relatively thin planar midweb in the core structure, said channels being opposite each other on the two faces Wherebyto provide on the two faces a plurality of opposed columnar studs of rectangular cross-section projecting from said midweb to the respective bounding faces of the core structure, and sheet material secured to each of the faces of the frame and to the corresponding end-faces of the studs.

5. A wooden panel suitable for use as a door comprising in combination a rectangular perimetric frame of wood, a core structure disposed Within the frame and fitting closely in the frame opening, said core structure having its bounding Yfaces cof-extensive with the faces of said frame, said core structure consisting of multitudinous pieces of wood placed together endwise and sidewise and glued into a unitary body, said pieces having their grains running generally in the .same direction and in the plane of the extent of the core structure, said pieces being in random arrangement of the annular rings of the individual pieces, said structure being provided with longitudinal and transverse channels in each face to a limited depth whereby to provide a relatively thin planar midweb in the core structure said channels being opposite each other on A8 the two faces -Whereby toV provide on the two faces a plurality of opposed columnar studs of rectangular cross-section projecting from said midweb to the respective bounding faces of the core structure, and at least two layers of crossbanded wood veneer secured to each of the faces of the frame and to the corresponding end-faces of the studs.

WILLARD H. RU'NDQUIST.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 823,843 Buyten June 19, 1906 1,356,764 Henderson Oct. 26, 1920 1,991,145 Fuchs et al Feb. 12, 1935 2,220,596 Bernhardt Nov. 5, 1940 2,302,487 Beiger et al. Nov. 17, 1942 FOREIGN PATENTS Number Country K Date 157,597 Great Britain Jan. 27, 1921 793,579 France 1935 148,015 Austria Dec. 10, 1936 

